The present invention concerns a method for the manufacture of novel branched polysiloxanes, more specifically a method for the manufacture of branched polysiloxanes comprised of the polysiloxane unit SiO.sub.4/2 as the branch center and a diorganopolysiloxane units as the branch.
Numerous proposals have been made for polysiloxanes having branches inside the molecules and they have been commerically available. For example, in W.H. Dickstein et al., Macromolecules, 22, 3886-3888 (1989), is reported the synthesis of branched polydimethylsiloxanes with 4 amino- group-terminated polydimethylsiloxy groups with controlled molecular weight. However, there have not been any reports of organopolysiloxanes having the polysiloxane unit SiO.sub.4/2 as the branch center.
Most of the known branched organopolysiloxanes are simple mixtures or reaction products of a SiO.sub.4/2 component and a diorganopolysiloxane component, and the structures are not clear. For example, H. Huang et al.: Polymer Bulletin, 14, 557-564 (1985) reported polymers obtained by reacting hydroxy-terminated dimethylpolysiloxane and tetraethyl orthosilicate by a sol-gel method. In this polymerization product, either ends of the diorganopolysiloxane can be bonded to the branch center, and the structure is not clear. There have not been any reports of so-called star-type organopolysiloxanes having polysiloxane a SiO.sub.2 unit as the branch center bonded to one end of diorganopolysiloxane components. We have proposed novel branched polysiloxanes and a method for their manufacture (Japanese Patent Application Nos. Hei 3{1991}-286745, Hei 3{1991}-286753).
As described above, the present invention provides a novel method for the manufacture of branched polysiloxanes with clear structure. These compounds are useful as starting materials for silicone elastomers or reinforcing agents. They are also useful as additives for improving flow characteristics of silicone fluids.